Datasheet TMP03, TMP04 (Analog Devices) - 10

TMP03/TMP04 APPLICATIONS INFORMATION TMP03 Output Configurations Supply Bypassing
The TMP03 (Figure 5a) has an open-collector NPN output Precision analog products, such as the TMP03, require a well- which is suitable for driving a high current load, such as an filtered power source. Since the TMP03 operate from a single 5 opto-isolator. Since the output source current is set by the pull- V supply, it seems convenient to simply tap into the digital logic up resistor, output capacitance should be minimized in TMP03 power supply. Unfortunately, the logic supply is often a switch- applications. Otherwise, unequal rise and fall times will skew the mode design, which generates noise in the 20 kHz to 1 MHz pulsewidth and introduce measurement errors. The NPN tran- range. In addition, fast logic gates can generate glitches hundred sistor has a breakdown voltage of 18 V. of millivolts in amplitude due to wiring resistance and induc- tance.
V+
If possible, the TMP03 should be powered directly from the
DOUT
system power supply. This arrangement, shown in Figure 3, will
TMP03 TMP04 DOUT
isolate the analog section from the logic switching transients. Even if a separate power supply trace is not available, however, gener- ous supply bypassing will reduce supply-line induced errors. Local supply bypassing consisting of a 10 µF tantalum electro- lytic in parallel with a 0.1 µF ceramic capacitor is recommended a. b. (Figure 4a). Figure 5. TMP03 Digital Output Structure The TMP04 has a “totem-pole” CMOS output (Figure 5b) and
TTL/CMOS
provides rail-to-rail output drive for logic interfaces. The rise
LOGIC
and fall times of the TMP04 output are closely matched, so that
CIRCUITS +10 F TMP03/
errors caused by capacitive loading are minimized. If load ca-
0.1 F TANT TMP04
pacitance is large, for example when driving a long cable, an external buffer may improve accuracy. See the “Remote Tem-
5V
perature Measurement” section of this data sheet for
POWER SUPPLY
suggestions. Figure 3. Use Separate Traces to Reduce Power Supply
Interfacing the TMP03 to Low Voltage Logic
Noise The TMP03’s open-collector output is ideal for driving logic gates that operate from low supply voltages, such as 3.3 V. As
5V
shown in Figure 6, a pull-up resistor is connected from the low voltage logic supply (2.9 V, 3 V, etc.) to the TMP03 output.
5V 50
Current through the pull-up resistor should be limited to about 1 mA, which will maintain an output LOW logic level of
V+ V+
<200 mV.
TMP03/ TMP03/ 10 F 0.1 F D D TMP04 OUT 10 F 0.1 F TMP04 OUT 3.3V 5V GND GND 3.3k V+ TO LOW VOLTAGE TMP03 DOUT
a. b.
LOGIC GATE INPUT
Figure 4. Recommended Supply Bypassing for the
GND
TMP03 The quiescent power supply current requirement of the TMP03 Figure 6. Interfacing to Low Voltage Logic is typically only 900 µA. The supply current will not change
Remote Temperature Measurement
appreciably when driving a light load (such as a CMOS gate), so When measuring a temperature in situations where high com- a simple RC filter can be added to further reduce power supply mon-mode voltages exist, an opto-isolator can be used to isolate noise (Figure 4b). the output (Figure 7a). The TMP03 is recommended in this application because its open-collector NPN transistor has a higher current sink capability than the CMOS output of the TMP04. To maintain the integrity of the measurement, the opto-isolator must have relatively equal turn-on and turn-off times. Some Darlington opto-isolators, such as the 4N32, have a turn-off time that is much longer than their turn-on time. In this case, the T1 time will be longer than T2, and an erroneous reading will result. A PNP transistor can be used to provide greater current drive to the opto-isolator (Figure 7b). An opto- isolator with an integral logic gate output, such as the H11L1 from Quality Technology, can also be used (Figure 8). –10– REV. B REV. B Document Outline RevHistory_TMP03_04.pdf REVISION HISTORY